It is well known that bipolar transistors, especially heterojunction bipolar transistors (HBTs) based on GaAs technologies, can exhibit excessive current leakage at emitter/base contact junctions. See Lin, Hao-Hsiung et. Al., “Super-gain AlGaAs/GaAs Heterojunction Bipolar Transistors using an Emitter Edge-thinning design,” Appl. Phys. Lett. 47 (8), 15 Oct. 1985, pp. 839-841. Surface recombination of electrons in the base material and the spacing between the emitter and base contacts of the devices degrade transistor performance and affect device reliability.
The prior art has attempted to minimize the parasitic capacitance at these emitter/base junction areas by, for example, producing devices 10 on a substrate 26. An area between the emitter layer 34 and the base contacts 48 is covered with a photoresist material 50 prior to etching the device as described in U.S. Pat. No. 5,804,877 (Fuller et. al.) and illustrated in FIG. 1. The disadvantage of this method is the use of an additional photolithography step during the device fabrication process that causes damage to collector sidewalls during the stripping of the photoresist and limits the useful operating voltage of the transistor.
To address the surface recombination problem that reduces the reliability of the HBTs, a fabrication process described in U.S. Pat. No. 5,001,534 (Lunardi et. al.) required that an emitter layer (referred to as a ledge) be left intact beneath the entire base contact and electrical contact to the base layer of the device was accomplished through the intact emitter layer. The base contact metal was diffused through the emitter layer, and the reliability of the transistors were compromised.
In U.S. Pat. No. 5,840,612 (Oki et. al.) surface passivation of HBTs was again addressed by using a depleted layer of widebandgap semiconductor (also referred to as a ledge) over the extrinsic base region of the transistor. The ledge thickness was defined by selectively etching away semiconductor layers above the widebandgap semiconductor; however, it is difficult to achieve a consistent ledge thickness and thus large variations in the device's characteristics result.
As demand for more reliable device performance continues to increase, the need for semiconductors, especially HBTs based on GaAs technologies, which exhibit maximum operating voltages has become apparent.
Accordingly, a need exists for a method of manufacturing a semiconductor component, and a semiconductor component thereof, that is both reliable and exhibits maximum operating voltages.
For simplicity and clarity of illustration, the figures illustrate the general invention, and descriptions and details of well-known features and techniques are omitted to avoid excessive complexity. The figures are not necessarily drawn to scale, and the same reference numerals in different figures denote the same elements. It is further understood that the embodiments of the invention described herein are capable of being manufactured or operated in other orientations than described or illustrated herein.